This film image released by The Weinstein Company shows Matt Bush, left, and Danielle Panabaker in a scene from "Piranha 3DD." (AP Photo/The Weinstein Company)
/ AP

LOS ANGELES 
Although a sequel to 2010's "Piranha 3D" seems entirely superfluous, don't tell that to the target demo of gorehounds and softcore-deprived teens (if they still exist) who may still take some notice. Regardless, the sub-par franchise installment "Piranha 3DD" will quickly sink beneath the waves to find a suitable resting place in video, where it will surely tempt younger viewers to outwit the R-rated restrictions.

After a brief newsreel recap of the bloody events depicted in "Piranha 3D," the follow-up introduces marine biology graduate student Maddy (Danielle Panabaker), returning home for the summer to find her skeezy step-dad Chet (David Koechner) reopening the formerly wholesome water park run by her deceased mother. Now known as "Big Wet," it's a destination better suited to grown-ups that's staffed with buxom lifeguards and former strippers.

Complete with an "Adults Only" swimming pool full of mostly naked women, Chet's relying on the overt sleaze factor and the piranha massacre at now-defunct Lake Victoria, site of "Piranha 3D," to drive summer business into his park. He's not leaving anything to chance however, hiring washed-up lifeguard celebrity David Hasselhoff (cheerfully spoofing himself) to open the park, sign autographs and pose for photos.

The reappearance of the killer fish in picturesque Cross Lake - appropriately located near "Merkin," Ariz. - sends Maddy in search of reclusive scientist Carl Goodman (Christopher Lloyd), with her hunky ex-boyfriend Kyle (Chris Zylka) and totally crushed-out co-worker Barry (Matt Bush) in tow. The kindly, if clearly depraved, researcher hypothesizes that the prehistoric fish may be migrating from deep in a network of underwater lakes and rivers to emerge in the vicinity of the water park.

That tipoff is enough to send Maddy on an investigation that uncovers Chet's scheme to avoid paying utility fees by extracting water from a subterranean aquifer, along with a whole hoard of hungry fish. By now, it's too late to stop the piranhas from invading the water park to wreak predictable havoc, despite the heroic interventions of Maddy, Henry and even Hasselhoff.

There was a time - back in the prehistory of the latter 20th century - when this type of Roger Corman-inspired, R-rated Z-movie served as a rite of passage for testosterone-toxified teens, before moving on to the greener pastures of university campuses and frat houses. With today's prevalence of online porn, amateur strippers and celebrity sex tapes, the target market is constantly shrinking, although the adequately handled 3D format, killer CGI fish and gore effects are still nominal selling points, however familiar by now.

As sequels go, "Piranha 3DD" has barely enough heft to squeeze out 83 minutes of ho-hum entertainment, although it faithfully delivers plenty of menacing fish and bouncing boobs, as amply advertised. Following up the Feast horror series, director John Gulager plays it mostly by the numbers and with an established template to work with, surprises aren't anticipated anyway, although tipping the follow-up is obviously required.

With most of the running time devoted to setting up and over-explaining the premise, mayhem gets short shrift. Performances are perfunctory overall, with even the slightly inspired cameos by Lloyd and Ving Rhames - returning as a local sheriff equipped with shotguns on his prosthetic legs - barely raising the temperature above tepid, although Hasselhoff seems eerily inspired in his willingness to ridicule his own image.